1. Field of the Invention
This invention is related to a method for neutralization of the explosive content of mines and unexploded ordnance ("UXO"). The invention also is related to apparatus used to practice the method.
2. Description of Related Art
Explosive-filled ordnance of divers type often must be destroyed or otherwise neutralized. Such ordnance includes not only unexploded shells, rockets, and fuses, but also ordnance that is designed to explode on contact or is triggered to explode by another activation mechanism, such as a detonator, such as a land, underwater, or shallow water mine. There exist many sources of UXO which must be destroyed. Ordnance that did not operate properly, that no longer is suitable for use, or that is surplus, are some examples of UXO that often must be destroyed or otherwise neutralized. A `land mine,` i.e., a mine placed on the Face, partially covered, or completely covered by ground and designed to explode upon contact or otherwise, is another example of a type of device that requires neutralization.
Neutralization can be required for various reasons. Unexploded shells, rockets, and fuses may be the result of ordnance that did not operate properly, for example, in a war zone or in a practice range. Surplus ordnance often is destroyed to avoid stockpiling unneeded quantities of ordnance, or as part of an arms reduction agreement. Mines often need to be neutralized to make a mined area safe for entry.
Known methods and apparatus for neutralizing UXO are not completely satisfactory.
One class of methods requires that the ordnance be taken to a central location for processing. For example, U.S. Pat. No. 5,434,335 discloses destruction of explosives and other `energetic` materials by feeding a stream of the material with diluent into a high temperature bath of molten alkali metal or alkaline earth metal salt. Organic material is destroyed, and inorganic material is separately recovered from the salt. Other destruction methods are known for particular types of material. For example, U.S. Pat. No. 3,916,805 and U.S. Pat. No. 5,516,971 are directed to destruction of nitrogenous explosives, the former by controlled oxidation and the latter by digestion in aqueous caustic solution. U.S. Pat. No. 5,523,517 is directed to destruction of nitramine explosive by heating a mixture of such explosive with an aqueous dispersion of powdered metal that does not react with water. Examples of suitable metals include aluminum, zinc, manganese, and magnesium. Controlled combustion of selected combinations of materials is disclosed in U.S. Pat. No. 5,463,169. Treatment of explosive waste is carried out in a bed of granular material, such as sand. The `energetic` material is ignited in the bed, and the granular material absorbs the force of any explosion, dampens the destructive power of propelled debris, and conveniently collects the unexploded debris.
As disclosed in U.S. Pat. No. 5,035,756, devices containing thermite (or Thermit.RTM.) mixtures (aluminum and Fe.sub.3 O.sub.4 powders) have been used to burn vent holes into the propellant/motor portion of ordnance carried on, e.g., aircraft for the purpose of venting the propellant during a fire. Thus venting the propellant is meant to preclude excessive pressure and explosion of the propellant during such a fire. This patent is directed to a thermite composition comprising particular components intended to yield selected density, tensile strength, and elasticity characteristics.
Another class comprises methods that can be applied to either material in ordnance or only to the explosive material removed from the ordnance. One such method is disclosed in U.S. Pat. No. 5,434,336. Sulfur and the explosive material are heated in an oxygen-free atmosphere to a temperature above 110.degree. C. for a time sufficient to degrade the material to non-explosive reaction products. When liquid sulfur is used and introduced to the reactor in a stream of solvent, particularly carbon disulfide (CS.sub.2), the UXO need not be dismantled before treatment. Use of a liquid sulfur stream is preferred with waxy or cast explosives, as the warm sulfur will soften the explosive and improve mixture thereof with the sulfur. However, in accordance with this method, an oxygen-free atmosphere must be maintained during the initial step. Then, thus-decomposed material is subjected to high temperature sulfur vapor to complete the destructive reaction.
Another class of methods is directed to reformulation of the `energetic` material. For example, U.S. Pat. No. 5,445,690 discloses a method for reformulating polymer and wax-bound explosives to improve, inter alia, brisance. Added materials can include oxidizer, plasticizer, and stabilizer.
None of the above-described methods is suitable for destruction or neutralization of UXO and mines in situ. Known methods of in situ destruction are unsatisfactory.
In one class of such methods, mines and UXO's are destroyed after detection by detonating a small explosive charge placed in or projected to the vicinity of the object to be destroyed. Detonation of this small charge causes a sympathetic detonation of the object and thus neutralizes the mine or UXO. Alternatively, a plurality of objects to be destroyed are removed from the site and relocated into one area, then detonated. This method requires use of an explosive charge and personnel skilled in the use of explosives. It also causes as much, if not more, property damage than the mine itself
Another class of methods of neutralizing UXO's and mines include use of plows, rollers, or flails attached to an armored vehicle. For example, U.S. Pat. No. 3,771,413 discloses use of wheels mounted on a vehicle, such as a tank, to detonate pressure-activated land mines buried in the ground in the path of the wheels. This method is slow, as the area to be cleared typically must be traversed a plurality of times, typically with the top layer of ground scraped away (itself a costly and dangerous undertaking) between traverses; cumbersome, as the necessary equipment must be sturdy, yet transportable from site to site; expensive, as it requires equipment and trained personnel; tedious, as a grid or other manner of ensuring thorough coverage must be established and adhered to assiduously, and dangerous, as the object is to cause the mines and UXO's to detonate.
A class of methods is directed to temporarily disabling mines and UXO's, typically by cooling them to a temperature at which it becomes inoperative. In U.S. Pat. No. 4,046,055, the case of the mine or UXO is penetrated so that liquid nitrogen can be injected therein. This method is unsatisfactory, as merely piercing the outside of the device may cause it to detonate. U.S. Pat. No. 3,800,715 discloses drawing a mine or UXO into a tubular shell, closing the ends, and introducing liquid nitrogen into the interior. This method is less than satisfictory because it requires that the explosive device be moved before it is made less dangerous. Whereas each of these methods requires that each object be treated individually, U.S. Pat. No. 5,140,891 discloses a method and apparatus for neutralizing mines and UXO's by spraying cryogenic material over the area to be cleared to render the materials at least temporarily inoperable. Ordnance removed by this method should be placed in liquid nitrogen as quickly as possible.
Another area-wide treatment is disclosed in U.S. Pat. No. 4,493,239. The area to be treated is infused with an electrolyte and subjected to a direct current voltage to enhance natural corrosion. The temperature of the area also may be increased, for example, by covering the area with black material, such as a plastic sheet, to further accelerate corrosion. This method is unsatisfactory because it takes on the order of five to ten years and requires continuing attention.
Thus, there exists a need for an easy, safe, and quick method for neutralizing mines and UXO's.